Ultrasonic method for imaging blood flow including disruption or activation of contrast agent

Abstract

An ultrasonic imaging system uses first and second perpendicular arrays. The first array is operated at high power to selectively destroy contrast agent suspended in flowing blood in discrete regions. The second array is used to image the alternating bands of contrast agent depleted blood and contrast image containing blood in order to allow blood flow characteristics to be assessed.

I claim: 
     
       1. An ultrasonic method for assessing flow characteristics in a vessel, said vessel comprising blood and a contrast agent, said method comprising the following steps: (a) transmitting sets of higher power ultrasonic signals into a first region of the vessel, said higher power ultrasonic signals operative to selectively disrupt the contrast agent in said first region of the vessel, to create a volume of blood in the vessel characterized by a reduced concentration of operative contrast agent; and   (b) imaging the contrast agent in a second region of the vessel, said second region including additional portions of the vessel not included in the first region and positioned downstream of the first region, said imaging step comprising the step of (b1) transmitting lower power ultrasonic signals into the second region of the vessel, said lower power ultrasonic signals disrupting the contrast agent to a lesser extent than said higher power ultrasonic signals.     
     
     
       2. The method of claim 1 wherein step (a) comprises the step of shaping the first region in a selected form corresponding substantially to a plurality of planes. 
     
     
       3. The method of claim 1 wherein step (a) comprises the step of shaping the first region in a selected form corresponding substantially to a plurality of intersecting planes. 
     
     
       4. An ultrasonic method for assessing flow characteristics in a vessel, said vessel comprising blood and a contrast agent, said method comprising the following steps: (a) transmitting sets of higher power ultrasonic signals into a first region of the vessel, said higher power ultrasonic signals operative to selectively activate the contrast agent in said first region of the vessel, to create a volume of blood in the vessel characterized by an enhanced concentration of operative contrast agent; and   (b) imaging the contrast agent in a second region of the vessel, said second region including additional portions of the vessel not included in the first region and positioned downstream of the first region, said imaging step comprising the step of (b1) transmitting lower power ultrasonic signals into the second region of the vessel, said lower power ultrasonic signals activating the contrast agent to a lesser extent than said higher power ultrasonic signals.     
     
     
       5. The method of claim 1 or 4 wherein step (a) comprises the step of applying a plurality of first transmit waveforms to a first transducer, wherein step (b1) comprises the step of applying a plurality of second transmit waveforms to a second transducer. 
     
     
       6. The method of claim 5 wherein the first transducer is oriented substantially perpendicular to the second transducer. 
     
     
       7. The method of claim 5 wherein at least one of the first and second transducers comprise a respective transducer array. 
     
     
       8. The method of claim 1 or 4 wherein the higher and lower power ultrasonic signals are positioned within a single frame, and wherein the higher power ultrasonic signals are positioned near a first edge of the frame. 
     
     
       9. The method of claim 1 or 4 wherein step (b1) comprises the step of selectively transmitting the lower power ultrasonic signals concentrated near a fundamental frequency; wherein step (b) further comprises the step of (b2) selectively receiving ultrasonic signals concentrated near a harmonic of the fundamental frequency; and wherein the contrast agent comprises a non-linear contrast agent. 
     
     
       10. The method of claim 1 or 4 comprising the further step of (c) using the contrast agent imaging of step (b) to assess blood flow velocity.   
     
     
       11. The method of claim 10 wherein step (c) comprises the step of providing a user-positioned caliper to mark regions of disrupted contrast agent. 
     
     
       12. The method of claim 10 wherein step (c) comprises the steps of (c1) creating a profile of imaged contrast agent, said profile extending through a plurality of regions of disrupted contrast agent; and   (c2) analyzing the profile to automatically determine a separation between two regions of disrupted contrast agent.   
     
     
       13. The method of claim 1 or 4 comprising the further step of (c) using the contrast agent imaging of step (b) to assess a blood flow profile across the vessel.   
     
     
       14. The method of claim 1 or 4 comprising the further step of (c) using the contrast agent imaging of step (b) to assess blood flow turbulence.   
     
     
       15. The method of claim 1 or 4 comprising the further step of (c) using the contrast imaging of step (b) to assess blood flow per heart beat cycle.   
     
     
       16. The method of claim 1 or 4 wherein step (a) comprises the step of varying a power level characteristic of the higher power ultrasonic signals in response to a user-controlled adjustment. 
     
     
       17. The method of claim 1 or 4 wherein step (a) comprises the step of varying a time interval between consecutive sets of said higher power ultrasonic signals in response to a user-controlled adjustment. 
     
     
       18. The method of claim 1 or 4 wherein step (a) comprises the step of varying a width of a spatial distribution of the higher power ultrasonic signals in response to a user-controlled adjustment. 
     
     
       19. The method of claim 1 or 4 wherein at least selected sets of the higher power ultrasonic signals sweep the first region of the vessel multiple times per set. 
     
     
       20. The method of claim 1 or 4 wherein at least selected sets of the higher power ultrasonic signals include first higher power ultrasonic signals focused at a first range and second higher power ultrasonic signals focused at a second range, different from the first range. 
     
     
       21. The method of claim 1 or 4 wherein step (a) comprises the step of synchronizing at least some of the sets of higher power ultrasonic signals with a selected portion of an EKG signal. 
     
     
       22. The method of claim 3 wherein the selected form is V-shaped. 
     
     
       23. The method of claim 3 wherein the selected form is X-shaped. 
     
     
       24. The method of claim 1 or 4 wherein step (a) is characterized by a duty cycle, and wherein the duty cycle of step (a) is greater than 50%. 
     
     
       25. The method of claim 1 or 4 wherein step (a) is characterized by a duty cycle, and wherein the duty cycle of step (a) is less than 50%.